Fuse plug



May 19, 1936. L, LUDWIG 2,041,295

FUSE PLUG Filed March 25, 1935 INVENTOR. 1 00.15 L ua/w/ BY gy ATTORNEYS.

Patented May 19, 1936 UNITED STATES PATENT OFFICE FUSE PLUG LouisLudwig, Brooklyn, N. Y. Application March 23, 1935, Serial No. 12,661

1 Claim.

My invention relates to fuse plugs of the type having an opening coveredwith transparent material through which the interior of the plug may beobserved. The invention has for its main objects to provide simple meanswithin such a fuse plug, immediately below the transparent opening,which will positively indicate whether or not the fuse is blown. Anotherobject is to provide positive means for assuring that the fusible linkwill always blow at a predetermined point. An additional object is to soconstruct these means that they will add but very slightly to the costof the fuse plug.

These and various other objects and advantages will be readilyunderstood from the following description and from the accompanyingdrawing, in which, however, various modifications may be made. In thedrawing Fig. 1 is a top view of a fuse constructed in accordance with myinvention,

Fig. 2 is a cross-sectional side View of Fig. 1,

Fig. 3 is another, but fragmental cross-sectional side view,

Fig. 4 is a disc used with the fuse,

Fig. 5 is a similar disc slightly modified,

Fig. 6 is a side View illustrating the manner in which either of thediscs, shown in Figs. 4 and 5, are attached to the fusible link of thefuse.

Fig. '7 is another top view of the fuse with parts broken away to showcertain details of construction, and

Fig. 8 a side View of Fig. '7.

I am aware that many indicating fuses have been invented in which adisc, or certain symbols imprinted on a disc, are caused to be destroyedor obliterated when the fuse is blown. In some cases this has beenaccomplished by using a fusible powder in combination with the disc andin others by discoloring or imprinting the disc with some fusiblematerial which will be discolored by the blowing of the fuse.

In other cases the gases and other products of combustion given off bythe blowing of the fusible link has been relied upon to so discolor thedisc as to indicate that the fuse has blown.

Repeatedly the blowing of such a fuse will fail to discolor the disc,either because the gases from the blowing of the fuse escaped toorapidly, or because the fusible link did not burn out on top of the discas expected to. The time element is too short and there is notsufficient air in the closed chamber to always discolor the disc.

The purpose of the present invention is to remedy these defects. Withthis in mind, reference is now had to all the views on the drawing onwhich the ordinary porcelain body of a fuse plug is shown at III, thethreaded metal ferrule at II, the cap at I2, the opening in the capthrough which the interior of the fuse may be observed at I3, theinterior recess at I4, and the transparent mica disc which covers theopening at I5.

The invention consists in bringing the fusible metal strip I6 right upto or. in very close proximity to, the mica disc and to place aninsulating disc I'I under the exposed part of the fusible strip in sucha manner that the smallest possible air pocket is formed between thisdisc and the mica disc. This I accomplished by slitting the disc in sucha manner that two tongues I8 and I9 are formed substantially in thecenterof the disc so that, when the disc is bent, as shown in Fig. 6,these tongues may be placed on opposite sides of the exposed part of thefusible strip and closed under this strip when the disc is go againstraightened out by being clamped between the body member and the micadisc. This construction forms very small air pockets 20 on oppositesides of the fusible strip, while it causes the rest of the disc tocontact with the mica disc. When the fusible strip blows, the very closeproximity to the mica of the point where it blows will cause the micadisc to become translucent, due to charring, and whatever gases aregenerated will discolor the indicating disc.

One end of the fusible metal is connected, in the usual manner, to thecenter contact 2| and the other end to the metal ferrule I I. The metalstrip is weakened, at the exposed part, as shown at 22. The correctwidth of this weakened part is all important if assurance is to be hadthat the fusible strip will always blow at this point. Many prior fusesof this type have failed because the strip would often blow below thedisc and not at the weakened part as anticipated.

I have discovered that to assure the certainty of the strip blowing atthe weakened part, the width of this part must not be greater than .065of one inch, (the gauge of the strip varying in thickness according tothe load the fuse is to carry.) I have alsofound it advisable to makethe weakened part comparatively long. In fact, I make it almost as longas the whole exposed part of the strip. With this construction, there isno danger, even with a slow overload on the fuse, that the strip willblow at any other place than within the pockets 20.

The disc Il may be made of any non-conduc ing material and I have foundthat ordinary stiff paper will serve very well. The disc may be madecircular, as shown in Fig. 4 and of a size to fit within the cap I 2,but I prefer to make it square or rectangular so that the corners 23will be clamped down between the cap I2 and the body part I0.Furthermore the square shape is cheaper to produce.

It will be noted that the two tongues form two shallow chambers one oneach side of the exposed part of the fusible strip. If symbols, such asfor example an O and a K, are imprinted, one on each of the tongues orin line with the tongues, it is evident that, when the fuse blows, thechambers formed by the tongues will direct the gases so that they willflow over these symbols and obliterate them.

What actually takes place is that the gases soot and partially scorchthe underside of the mica disc and the upper side of the paper disc. Asthis sooting and scorching takes place over and in line with the tonguesit is evident that the symbols are sure to be obscured. In other words,a sooted streak is formed across the mica disc which will show veryplainly, even when the mica disc is quite dirty and dusty as it may befrom long use. The gases finally escape into the interior of the fusethrough the opening of the tongues.

Figs. 7 and 8 illustrate the manner in which the fuse is vented so thatthe gases may escape from it without any fire hazard. The upper face ofthe body member ID is scored with a number of grooves at right angles toeach other so as to form a plurality of raised points with a pluralityof tortuous channels between them, as shown at 24. After the gases enterthe interior chamber M, they are free to escape through these tortuouschannels, still, if the gases should be ignited, the flame will beextinguished before it can pass through the channels.

The paper discs may be made in various colors to indicate the capacityof the fuse or the capacity may be imprinted on the disc, as shown inFigs. 4 and 5.

From the foregoing it -will be seen that this construction contains theessential elements for assuring the correct operation of the fuse. Theshallow pockets not only prevent too rapid dissipation of the gases, buteffectively direct them over the parts which are to be obscured. Thetongues prevent excessive pressure on the mica disc, the correctweakening of the fusible link assures it blowing out at the correctplace, and the channels remove any danger of fire. Furthermore, the onlyaddition to the ordinary fuse is the paper disc which can bemanufactured at very low cost and inserted without altering the ordinaryassembling processes of the fuse.

Having described my invention and its objects, what I claim as new andwish to protect by Letters Patent is:

The combination with a fuse plug of the type comprising a one-piece bodymember made of insulating material and having an interior recess coveredwith a transparent disc, a threaded metal shell secured on the outsideand. a metal contact secured in the bottom; of a fusible metal stripunder said strip to form shallow pockets on both sides thereof, saiddisc clamped between the end of the body member and the transparentdisc, and the fusible strip having a weakened portion contained withinsaid pockets.

LOUIS LUDWIG.

